Messages in this thread | | | Subject | Re: bisected: futex regression >= 3.14 - was - Slowdown due to threads bouncing between HT cores | From | Mike Galbraith <> | Date | Wed, 08 Oct 2014 19:59:44 +0200 |
| |
On Wed, 2014-10-08 at 13:04 -0400, Linus Torvalds wrote: > On Wed, Oct 8, 2014 at 11:37 AM, Mike Galbraith > <umgwanakikbuti@gmail.com> wrote: > > > > 11d4616bd07f38d496bd489ed8fad1dc4d928823 is the first bad commit > > commit 11d4616bd07f38d496bd489ed8fad1dc4d928823 > > Author: Linus Torvalds <torvalds@linux-foundation.org> > > Date: Thu Mar 20 22:11:17 2014 -0700 > > > > futex: revert back to the explicit waiter counting code > > While that revert might make things a tiny bit slower (I hated doing > it, but the clever approach sadly didn't work on powerpc and depended > on x86 locking semantics), I seriously doubt it's really relevant. > It's more likely that the *real* problem itself is very > timing-dependent, and the subtle synchronization changes here then > expose it or hide it, rather than really fixing anything. > > So like Thomas, I would suspect a race condition in the futex use, and > then the exact futex implementation details are just exposing it > incidentally.
Whew, good, futex.c is hard. Heads up chess guys <punt>.
-Mike
| |